Twenty-five pixel averages of the DN values (an 8 bit, unsigned integer for
each pixel in the SAR image) of a representative location on the crater floor
(dni) and a location in the terrain surrounding the crater (dno). A
representative location in the crater floor is similar in brightness to the
majority of the crater floor. A representative location in the terrain
surrounding the crater is a piece of terrain near the crater that is similar in
character to the terrain that the crater formed on but that is unaffected by
the crater. Within the crater we chose a piece of floor that appeared to be
similar in brightness to the majority of the floor material. The difference
between these values (dnd) gives an estimate of the relative radar brightness
of the crater interior. Individual DN values can be converted to radar cross
section in decibels by the formula:

One DN equals 0.2 dB of radar
backscatter.

The average DN is the average of the logaritm of the
backscatter at each pixel location. This calculation was only made for craters
> 16 km in diameter.